The technique of microinjection will be used to study the biological activities of avian oncornaviral RNAs. Previous work has shown that the ability of an RNA preparation to function as viral envelope-glycoprotein messenger (env mRNA) is indicated by the number of infectious virus released following injection into cells infected by the envelop-deficient Bryan strain of Rous sarcoma virus (RSV). This assay for env mRNA will be employed to determine the capacity of virus particles to encapsulate 21S env mRNA from infected cells. The type of association between this mRNA and other virion RNA molecules will be analyzed along with the possibility that the viron encapsulated env mRNA can be converted into subgenomic DNA following infection. This information will be related to the ability of microinjected env mRNA to become expressed persistently by RSV infected cells. This phenomenon is believed to occur when microinjected env mRNA becomes encapsulated into virus particles released from injected cells which then infect neighboring cells in such a way that the injected mRNA is converted into DNA. Biological and chemical analyses are designed to verify this hypothesis. A study of the nuclear generation of env mRNA from virion 35S RNA will be continued and expanded to include biochemical evidence that such a conversion takes place. Finally, attempts will be made to develop an assay for products of the viral sarcomagenic gene.